Outbreaks of salmonella and norovirus in Helensburgh were being investigated by health experts this week.
NHS Highland says the salmonella infection is only associated with the fee-paying Lomond School, where several other pupils are also reported to have gastrointestinal upset.
Officials stress that the wider community is not thought to be at risk from the salmonella outbreak, and say control measures have already been put in place to ensure that no possible food source will be used again.
A statement said although the source had not been identified, no-one had become unwell at the school and developed new symptoms of salmonella since Friday last week.
Norovirus is said to be circulating in the Helensburgh area and it is thought that some of those with gastrointestinal upset at the school may have norovirus rather than salmonella. Samples are being collected to obtain a definitive diagnosis.
An outbreak control team meeting was held yesterday (Tuesday) with Argyll and Bute Council environmental health officers and the school’s headteacher, nurse and catering manager.
NHS Highland public health medical consultant Dr Ken Oates, who chaired the outbreak control team, said: “The school and the people involved in this incident have given us their full co-operation and responded in an effective manner.
“We are working closely with our colleagues in Argyll and Bute Environmental Health and are confident that this outbreak is under control and poses no ongoing risk to the wider school community or the general public.
“We will continue our efforts to identify the cause and ensure that measures are taken to prevent a recurrence.”
A statement by school headteacher Simon Mills said: “A number of members of the school community were ill over the last week and it is important that everyone at school is fully updated on this issue.
“We have had the ongoing support of the NHS and they continue to be very helpful in ensuring that all aspects of this issue are fully addressed.
“We are pleased to see the affected pupils returning to lessons at school.”